This application claims priority and benefit of Korean Patent Application No. 2001-68840, filed on Nov. 6, 2001, the contents of which are incorporated herein by reference in their entirety.
The present invention relates to a synchronous semiconductor memory device, and more particularly, to a data input circuit and method of inputting data to a synchronous semiconductor memory device.
A semiconductor memory device may be used as a main memory in a computer system for input and output of data into and from memory cells of the memory device. The data input/output speed of a semiconductor memory device may be very important in deciding an operating speed of a computer system. As a result, there have been continual efforts to improve the operating speeds of semiconductor memory device.
As a result of these efforts, a synchronous dynamic random access memory (SDRAM) has evolved to include internal circuits that control memory operations in synchronization with a clock signal of, e.g., a computer system. Examples of SDRAM may include a single data rate SDRAM (SDR SDRAM) and a double data rate SDRAM (DDR SDRAM). The SDR SDRAM may input or output one data per cycle of a clock signal responsive to a rising or falling edge of the clock signal. On the other hand, the DDR SDRAM may input or output two data per cycle of a clock signal to a first rising edge and then a falling edge of the clock signal. That is, the bandwidth of the DDR SDRAM may be twice that of the SDR DRAM.
With twice the transfer rate, the DDR SDRAM may be understood to have a window of opportunity for transfer of data to/from the DDR SDRAM that is smaller than that of the SDR SDRAM. To accommodate the smaller windows, a data strobe signal may be used to assist controlled retrieval of data from an input/output data signal. Thus, the DDR SDRAM may include an extra pin to allow input of the data strobe signal.
FIG. 1 is a block diagram of a data input circuit for a conventional synchronous semiconductor memory device. Referring to FIG. 1, data input circuit 100 includes data input buffer 110, data delay circuit 112, data fetch circuit 120, synchronous circuit 140, data strobe buffer 160, first delay circuit 162, a second delay circuit 164, clock input buffer 180, and auto pulse generation circuit 182. An external input data signal DIN, an external data strobe signal DS, and an external clock signal CLK may be applied to inputs of data input buffer 110, data strobe buffer 160, and clock input buffer 180, respectively.
During operation of data input circuit 100, data may be fetched from an internal data signal PDIND responsive to data strobe signal PDSD1. The fetched signal may then be converted into two separate internal parallel data signals DI_F and DI_S. Data may then be fetched from the internal parallel data signals DI_F and DI_S in response to the data strobe signal PDSD2 further delayed and may then be synchronized with an internal clock signal PCLK2 to provide parallel data signals DIN_F and DIN_S.
A phase difference between the external data strobe signal DS and the external clock signal CLK may cause variations of up to a half cycle between the two. A technical standard tDQSS may indicate a timing margin between the external clock signal CLK and the external data strobe signal DS, which may include two different cases: CASE1 and CASE2. In a first case, the technical standard tDQSS may be 0.75 tCK (hereinafter, referred to as tDQSS_MIN) and the phase of the external data strobe signal DS may lead that of the external clock signal CLK by tCK/4. In a second case, the technical standard tDQSS may be 1.25 tCK (hereinafter, referred to as tDQSS_MAX) and the phase of the external data strobe signal DS may lag that of the external clock signal CLK by tCK/4. Here, tCK represents a duration of one period or one cycle of the external clock signal CLK.
FIG. 2 is a timing diagram useful for describing exemplary operations of the data input circuit of FIG. 1 for examples where the cycle of the external clock signal CLK may be relatively large. Referring to FIG. 2, the first case of operation (CASE1) shows operation of data input circuit 100 where the technical phase standard is tDQSS_MIN. The second case of operation (CASE2) shows operation of the data input circuit 100 where the technical standard is tDQSS_MAX. Further referencing FIG. 2, a data set-up time tDS may reference a duration required for set-up of data and a data hold time tDH a duration required for data of an external input data signal DIN to be presented or held at an input relative to a rising edge of the data strobe signal DS. Internal parallel data signals DII_F and DII_S represent internal data signals from which the internal parallel data signals DI_F and DI_S may be fetched by the second internal data strobe signal PDSD2.
In the first case, CASE1 of tDQSS_MIN, the phase of the external data strobe signal DS leads that of the external clock signal CLK by tCK/4. In order to synchronize the external input data signal DIN as fetched by the external data strobe signal DS with the phase of the external clock signal CLK, it may be understood that a seemingly large delay may be required between the edge of the internal data strobe signal PDSD1 and that of the internal data strobe signal PDSD2. This delay time T1 as shown in FIG. 2 should be large enough in order to allow retrieval of valid data from the respective data signal.
In the second case CASE2 of tDQSS_MAX, the phase of the external data strobe signal DS may lag that of the external clock signal CLK by tCK/4. In order to synchronize the external input data signal DIN fetched by the external data strobe signal DS with the external clock signal CLK, a small delay may be needed between edges of the internal data strobe signal PDSD1 and the internal data strobe signal PDSD2 to allow retrieval of valid data from the data signal. This delay time T2 as shown in FIG. 2 might need to be less than that of the first case.
However, the conventional data input circuit 100 may use a fixed delay for the establishment of the second internal data strobe signal PDSD2 relative the first PDSD1. As a result, the operating characteristics for the above-mentioned cases of tDQSS_MIN and tDQSS_MAX may remain fixed and may compromise synchronization at the two different extremes. That is, since the delay duration that is used for establishing the second internal data strobe signal PDSD2 from the first PDSD1 may be fixed, regardless of a cycle length or frequency of the clock signal, the timing margin due to this fixed delay duration may become insufficient when the cycle length of the external clock signal CLK decreases as the operating frequency increases.
FIG. 3 is a timing diagram useful for describing an operation of the conventional data input circuit of FIG. 1 when the cycle of the external clock signal CLK may be relatively small. It may be observed from the exemplary depictions of FIG. 3 that synchronization data failures may result during the short cycle clock operations of the conventional data input circuit 100.
For example, for the case of tDQSS_MIN (CASE1), variations in process, voltage, and/or temperature may cause the duration T1 for the delay associated with generating the second internal data strobe signal PDSD2 from the first PDSD1 to decrease. Under certain conditions, such reductions may interfere with the effective generation of internal parallel data signals DIN0 and DIN1 in the CASE1 conditions.
In another example for the case of tDQSS_MAX (CASE2), variations in process, voltage, and/or temperature may cause the duration T2 associated with the delay for generating of the second internal data strobe signal PDSD2 from the first PDSD1 to increase. Such increases might then cause generation of invalid data under the CASE2 conditions.
Addressing some of the above problems, embodiments of the present invention may provide a data input circuit and associated methods of operations for a synchronous semiconductor memory device. The embodiments may control a delay duration for generation of a data strobe signal according to a phase relation between the data strobe signal and a clock signal. The controlled duration may allow for effective synchronization of an input data signal fetched by the data strobe signal to the clock signal.
Accordingly to one embodiment of the present invention, a data input circuit for a synchronous semiconductor memory device may comprise a detection unit for detecting whether the phase of a data strobe signal may lead or lag that of a clock signal. A delay unit may delay the data strobe signal by a first duration when the phase of the data strobe signal leads that of the clock signal. Or, the delay unit may delay the data strobe signal by a second duration when the phase of the data strobe signal may lag that of the clock signal. A data input synchronization unit may synchronize an input data signal fetched by the data strobe signal. The fetched signal may be synchronized to the clock signal responsive to the delayed data strobe signal output by the delay unit.
In a further embodiment, the detection unit may determine a phase difference between the data strobe signal and the clock signal of up to one fourth of a cycle of the clock signal. Additionally, the duration established for the first delay may be larger than the duration for the second delay.
According to another embodiment of the present invention, a data input circuit for a synchronous semiconductor memory device may comprise a data buffer to receive an external input data signal and to buffer the received signal for generating a first internal input data signal. A data strobe buffer may receive an external data strobe signal and buffer the received data strobe signal to generate a first internal data strobe signal. A clock buffer may receive and buffer an external clock signal to generate a first internal clock signal and/or second internal clock signal. A data delay circuit may delay the first internal input data signal to generate a second internal input data signal. A first strobe delay circuit may delay the first internal data strobe signal to generate a second internal data strobe signal. A detection circuit may detect whether the phase of the first internal data strobe signal may lead or lag that of the first internal clock signal and may generate a detection signal based on the detection. A data fetch circuit may fetch the second internal input data signal in synchronous relationship with respect to the second internal data strobe signal for generating a first strobe synchronous data signal. A second delay circuit may delay the second internal data strobe signal with a duration established by the detection signal for generating a third internal data strobe signal. A synchronization circuit may synchronize the first stage synchronous data signal to be in synchronous relationship with respect to, firstly, the third internal data strobe signal and, subsequently, the second internal clock signal for generating a second stage synchronous data signal.
In a further embodiment, the detection circuit may comprise a first transmission unit to transmit, responsive to the first internal data strobe signal, the first internal clock signal to a first latch unit. The first latch unit may receive and latch the first internal clock signal transmitted thereto by the first transmission unit. A second transmission unit may be operable to transmit, responsive to the first internal data strobe, the first internal clock signal latched by the first latch unit to a second latch unit. The second latch unit may latch the first internal clock signal that may be transmitted thereto by the second transmission unit. An AND circuit may perform an AND operation of the first internal clock signal latched by the second latch unit with an internal write signal. The write signal may be derived from a write operation of the synchronous semiconductor memory device. The output of the AND circuit may serve as the detection signal provided by the detection circuit to the second delay circuit.
In another embodiment, the second delay circuit may comprise a first NAND gate that may invert and perform an AND operation of an inverted representation of the detection signal with the second internal data strobe signal after it has been propagated through and delayed by an inverter chain. A second NAND gate may invert and perform an AND operation of the detection signal with the second internal data strobe signal that may have similarly been propagated through and delayed by the inverter chain. An OR circuit may be operative to output one of the output signals of the first and second NAND gates in which one of the output signals of the first NAND and second gates may be delayed by a predetermined duration relative the other. The output of this OR circuit may serve as the third internal data strobe signal.
According to another embodiment of the present invention, a method of inputting data to a synchronous semiconductor memory device may comprise detecting whether the phase of a data strobe signal may lead or lag that of a clock signal. The data strobe signal may be delayed by a first duration when the detecting determines that the phase of the data strobe signal may lead that of the clock signal. Alternatively, the data strobe signal may be delayed by a second duration when the detecting determines that the phase of the data strobe signal may lag that of the clock signal. A data signal may be, firstly, fetched in synchronous relationship to the data strobe signal. The fetched data signal may then be synchronized with reference to the delayed strobe signal and, thereafter, to the clock signal.
In one embodiment, the detecting may determine a phase difference between the data strobe signal and the clock signal of up to one-fourth of a cycle of the clock signal and the duration of the first delay may be longer than that of the second delay.
In exemplary embodiments, the data input circuit and its method of operation can effectively synchronize an input data signal with a clock signal, even for clock signals of small cycle or high frequency.